1. Field of the Invention
This invention pertains to switching devices for connecting high voltage, high-energy sources to gas discharge lasers so as to discharge high currents in short times through the gas laser medium. More particularly, this invention pertains to railgap switches for use as switching devices in pulse discharge gas laser systems.
2. Description of the Prior Art
FIG. 1 depicts a prior art, railgap switch (1). The switch consists of an elongated metal blade (2) that is located adjacent to elongated bar (3) and which blade is separated from the bar along the elongated length of blade (2) and bar (3) by a small distance or gap (4). Bar (3) typically is attached to plate (5). Blade (2), bar (3) and plate (5) all are made of conducting materials. A housing (6) made of an insulating material maintains the position of blade (2) relative to bar (3), and encloses gas (7), which gas fills the volume enclosed thereby, including the gap between blade (2) and bar (3). A gas mixture such as one composed of 10 percent argon and 90 percent nitrogen molecules (N.sub.2) typically is used in the prior art devices. Typically, blade (2) has a thickness of the order of 0.5 millimeters, bar (3) has a diameter of 2 centimeters, the gap (4) is from 0.5 to 2 centimeters in width, and the blade (2) and bar (3) are from 20 centimeters to 1 meter in length.
FIG. 2 shows in cross section, the shape of blade (2) and bar (3) and their relative positions. In operation, a sufficiently high voltage is applied to blade (2), relative to bar (3), to cause the gas in gap (4) to breakdown and form a series of conducting arcs between the blade and bar along their elongated lengths. The initial formation of the arcs may be encouraged by partially pre-ionizing the gas with ultra-voilet or other radiation. Once the arcs are formed, the arcs act, in effect, to connect blade (2) electrically to bar (3), thus, forming a relatively low resistance and low inductance path for the high currents required for exciting pulse discharge gas lasers.
The relatively thin shape of the edge (8) of blade (2), acts, in the initial stage of the formation of arcs between the blade and bar, to concentrate and intensify the electric fields near edge (8), which in turn, reduces the voltage required to initiate arc formation and also causes the arcs to form along edge (8). Repeated operation of the switch at high current densities, however, causes edge (8) of blade (2) to be ablated, thus, effectively increasing the size of the gap between blade (2) and bar (3), as a consequence, changing the electrical characteristics of the switch. Eventually, the ablation of blade (2) is sufficient to require replacement of the blade.